JP6460934B2 - Imaging lens and imaging apparatus - Google Patents

Description

  The present invention relates to an imaging lens suitable for an endoscope, a vehicle-mounted camera, a surveillance camera, and the like, and an imaging device including the imaging lens.

  2. Description of the Related Art Conventionally, in the medical field, an insertion type endoscope in which a long insertion portion having an imaging device built in a distal end portion thereof is inserted from a subject's mouth, nose or the like to image a body cavity has become widespread. As an imaging lens that can be used in such an endoscope, for example, those described in Patent Documents 1 and 2 below are known.

  In addition to such an endoscope, as fish-eye lenses that can be used for in-vehicle cameras, surveillance cameras, and the like, for example, those described in Patent Documents 3 to 4 below are known.

  Patent Documents 1 to 4 all disclose a lens system including a front group, an aperture stop, and a rear group.

Japanese Patent No. 5006476 Japanese Patent No. 5565560 Japanese Patent Publication No. 51-002826 Japanese Patent Publication No.51-014017

  However, since the lens systems disclosed in Patent Documents 1 to 4 are not sufficiently corrected for various aberrations, there is a need for an imaging lens in which various aberrations are favorably corrected.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an imaging lens in which various aberrations are favorably corrected and an imaging apparatus including the imaging lens.

  The imaging lens of the present invention is substantially composed of a front group, an aperture stop, and a rear group having a positive refractive power in order from the object side, and the front group includes two or more negative lenses in order from the object side. And a negative lens and a cemented lens in which one positive lens having a d-line (wavelength 587.6 nm) reference Abbe number smaller than the negative lens is cemented in this order from the object side, The rear group is substantially composed of one or more positive lenses in order from the object side, and a cemented lens having one positive lens and one negative lens in this order from the object side and having a positive refractive power as a whole. It is characterized by becoming.

In the imaging lens of the present invention, it is preferable that the following conditional expression (1) is satisfied. In addition, it is more preferable to satisfy the following conditional expression (1-1).
0.30 <f / fb <0.70 (1)
0.40 <f / fb <0.60 (1-1)
However,
f: focal length of entire system fb: focal length of rear group

Moreover, it is preferable that the following conditional expression (2) is satisfied. In addition, it is more preferable to satisfy the following conditional expression (2-1).
30.00 <νd (R1) −νd (R2) <80.00 (2)
35.00 <νd (R1) −νd (R2) <75.00 (2-1)
However,
νd (R1): Abbe number of the positive lens in the rear group cemented lens νd (R2): Abbe number of the negative lens in the rear group cemented lens

Moreover, it is preferable that the following conditional expression (3) is satisfied. In addition, it is more preferable to satisfy the following conditional expression (3-1).
−3.00 <f / fn <−0.90 (3)
−2.50 <f / fn <−1.10 (3-1)
However,
f: focal length of the entire system fn: composite focal length of two or more negative lenses in the front group (negative lenses excluding the cemented lens in the front group)

  The front group preferably has negative refractive power.

Moreover, it is preferable that the following conditional expression (4) is satisfied. In addition, it is more preferable to satisfy the following conditional expression (4-1).
-0.90 <f / fa <0.00 (4)
−0.80 <f / fa <−0.10 (4-1)
However,
f: focal length of the entire system fa: focal length of the front group

Moreover, it is preferable that the following conditional expression (5) is satisfied. In addition, it is more preferable to satisfy the following conditional expression (5-1).
0.00 <νd (F1) −νd (F2) <30.00 (5)
0.00 <νd (F1) −νd (F2) <23.40 (5-1)
However,
νd (F1): Abbe number of the negative lens in the cemented lens in the front group νd (F2): Abbe number of the positive lens in the cemented lens in the front group

  Further, it is preferable that the rear group substantially includes a positive lens and a cemented lens in which a positive lens and a negative lens are cemented in this order from the object side.

The front group may be substantially composed of two negative lenses in order from the object side, and a cemented lens in which a negative lens and a positive lens are cemented in this order from the object side .

  An image pickup apparatus of the present invention includes the above-described image pickup lens of the present invention.

  In addition, the above-mentioned “consisting essentially of” means a lens having substantially no power other than those listed as constituent elements, an optical element other than a lens such as a diaphragm, a mask, a cover glass, and a filter, and a lens. It is intended that a mechanism part such as a flange, a lens barrel, an image sensor, a camera shake correction mechanism, and the like may be included.

  Further, the sign of the lens surface shape, the radius of curvature, and the refractive power is considered in the paraxial region when an aspheric surface is included.

  The imaging lens of the present invention is substantially composed of a front group, an aperture stop, and a rear group having a positive refractive power in order from the object side, and the front group includes two or more negative lenses in order from the object side. And a negative lens and a cemented lens in which one positive lens having a d-line (wavelength 587.6 nm) reference Abbe number smaller than the negative lens is cemented in this order from the object side, The rear group is substantially composed of one or more positive lenses in order from the object side, and a cemented lens having one positive lens and one negative lens in this order from the object side and having a positive refractive power as a whole. Therefore, it is possible to obtain an imaging lens in which various aberrations are favorably corrected.

  Moreover, since the imaging device of the present invention includes the imaging lens of the present invention, it is possible to acquire a high-quality image.

Sectional drawing which shows the lens structure of the imaging lens (common with Example 1) concerning one Embodiment of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 2 of this invention. Each aberration diagram of the imaging lens of Example 1 of the present invention Each aberration diagram of the imaging lens of Example 2 of the present invention 1 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram illustrating another aspect of an imaging apparatus according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a lens configuration of an imaging lens according to an embodiment of the present invention. The configuration example shown in FIG. 1 is the same as the configuration of the imaging lens of Example 1 described later. In FIG. 1, the left side is the object side, and the right side is the image side. The illustrated aperture stop St does not necessarily indicate the size or shape, but indicates the position of the stop on the optical axis Z. Further, the axial light beam wa and the light beam wb having the maximum field angle are also shown.

  As shown in FIG. 1, the imaging lens is substantially composed of a front group G1, an aperture stop St, and a rear group G2 having a positive refractive power in order from the object side.

  FIG. 1 shows an example in which an optical member PP having an incident surface and an output surface parallel to each other is disposed between the rear group G2 and the image plane Sim. The optical member PP assumes an optical path conversion prism, a filter, a cover glass, and the like for bending the optical path, and a configuration in which the optical member PP is omitted is also possible in the present invention. When the optical path conversion prism is used, the optical path is a bent optical path. However, for easy understanding, FIG. 1 shows a developed optical path.

  The front group G1 includes, in order from the object side, two or more negative lenses, one negative lens, and one positive lens having a d-line (wavelength 587.6 nm) reference Abbe number smaller than that of the negative lens. It consists essentially of a cemented lens cemented in this order from the side.

  Thus, by arranging two or more negative lenses in order from the most object side of the front group G1, it is possible to contribute to widening of the angle and to suppress curvature of field. Further, by using only one pair of cemented lenses on the image side of the two or more negative lenses in the front group G1, it is possible to prevent the total length and aperture of the front group G1 from becoming long, and to improve the eccentric sensitivity. It is possible to satisfactorily correct axial chromatic aberration and chromatic aberration of magnification while suppressing it. In particular, when the imaging lens of the present invention is applied to an endoscope, it is preferable that the imaging lens is small and has a small diameter, and thus the aspect of the present invention is suitable.

  The rear group G2 includes, in order from the object side, one or more positive lenses, and a cemented lens having one positive lens and one negative lens cemented in this order from the object side and having a positive refractive power as a whole. It is structured.

  Thus, spherical aberration can be suppressed by arranging one or more positive lenses in order from the most object side of the rear group G2. Further, by arranging the above-mentioned cemented lens on the most image side of the rear group G2, the cemented lens moves away from the aperture stop St and the height at which the peripheral rays pass is increased, so that the axial chromatic aberration is not excessively corrected. In addition, the effect of correcting the lateral chromatic aberration can be enhanced. Furthermore, by making the cemented lens of the rear group G2 have a positive refractive power, it is possible to suppress the incident angle of the principal ray at the peripheral field angle to the image plane.

In the imaging lens of the present embodiment, it is preferable that the following conditional expression (1) is satisfied. By ensuring that the lower limit of conditional expression (1) is not exceeded, it is possible to achieve both ensuring of back focus and shortening of the overall length. In addition, curvature of field can be suppressed by avoiding exceeding the upper limit of conditional expression (1). If the following conditional expression (1-1) is satisfied, better characteristics can be obtained.
0.30 <f / fb <0.70 (1)
0.40 <f / fb <0.60 (1-1)
However,
f: focal length of entire system fb: focal length of rear group

Moreover, it is preferable that the following conditional expression (2) is satisfied. By preventing the lower limit of conditional expression (2) from being reached, lateral chromatic aberration can be suppressed. In addition, axial chromatic aberration can be suppressed by preventing the conditional expression (2) from exceeding the upper limit. If the following conditional expression (2-1) is satisfied, better characteristics can be obtained.
30.00 <νd (R1) −νd (R2) <80.00 (2)
35.00 <νd (R1) −νd (R2) <75.00 (2-1)
However,
νd (R1): Abbe number of the positive lens in the rear group cemented lens νd (R2): Abbe number of the negative lens in the rear group cemented lens

Moreover, it is preferable that the following conditional expression (3) is satisfied. By making it not be below the lower limit of conditional expression (3), curvature of field can be suppressed. In addition, the viewing angle can be increased by preventing the conditional expression (3) from exceeding the upper limit. If the following conditional expression (3-1) is satisfied, better characteristics can be obtained.
−3.00 <f / fn <−0.90 (3)
−2.50 <f / fn <−1.10 (3-1)
However,
f: focal length of the entire system fn: composite focal length of two or more negative lenses in the front group (negative lenses excluding the cemented lens in the front group)

  The front group G1 preferably has negative refractive power. With such a configuration, back focus can be secured.

Moreover, it is preferable that the following conditional expression (4) is satisfied. By avoiding the lower limit of conditional expression (4) from being reached, curvature of field can be suppressed. In addition, the viewing angle can be increased by avoiding exceeding the upper limit of conditional expression (4). If the following conditional expression (4-1) is satisfied, better characteristics can be obtained.
-0.90 <f / fa <0.00 (4)
−0.80 <f / fa <−0.10 (4-1)
However,
f: focal length of the entire system fa: focal length of the front group

Moreover, it is preferable that the following conditional expression (5) is satisfied. By preventing the lower limit of conditional expression (5) from being reached, chromatic aberration of magnification can be suppressed. Also, axial chromatic aberration can be suppressed by avoiding exceeding the upper limit of conditional expression (5). If the following conditional expression (5-1) is satisfied, better characteristics can be obtained.
0.00 <νd (F1) −νd (F2) <30.00 (5)
0.00 <νd (F1) −νd (F2) <23.40 (5-1)
However,
νd (F1): Abbe number of the negative lens in the cemented lens in the front group νd (F2): Abbe number of the positive lens in the cemented lens in the front group

  In addition, it is preferable that the rear group G2 substantially includes a positive lens and a cemented lens in which a positive lens and a negative lens are cemented in this order from the object side. Thus, by comprising from three lenses, it can be set as the imaging lens which has desired performance with a small number of lenses. Note that the most object-side positive lens has an effect of suppressing spherical aberration. In addition, the cemented lens has an effect of suppressing lateral chromatic aberration.

  Further, the front group G1 may be substantially composed of two negative lenses in order from the object side, and a cemented lens in which the negative lens and the positive lens are cemented in this order from the object side. Thus, by comprising four lenses, it is possible to obtain an imaging lens having desired performance with a small number of lenses. The two negative lenses closest to the object have the effect of suppressing field curvature. In addition, the cemented lens has an effect of suppressing axial chromatic aberration and lateral chromatic aberration.

  The front group G1 may be substantially composed of three negative lenses in order from the object side, and a cemented lens in which the negative lens and the positive lens are cemented in this order from the object side. In this case, although the number of negative lenses is increased as compared with the aspect in which the front group G1 is composed of four lenses as described above, it is advantageous for widening the angle.

  In addition, when the imaging lens is used in a harsh environment, a protective multilayer coating is preferably applied. Further, in addition to the protective coat, an antireflection coat for reducing ghost light during use may be applied.

  Also, when this imaging lens is applied to an imaging device, various types such as a cover glass, a prism, an infrared cut filter, and a low-pass filter are provided between the lens system and the image plane Sim depending on the configuration of the camera side on which the lens is mounted. It is preferable to arrange a filter. Instead of arranging these various filters between the lens system and the image plane Sim, these various filters may be arranged between the lenses, or various filters and You may give the coat | court which has the same effect | action.

Next, numerical examples of the imaging lens of the present invention will be described.
First, the imaging lens of Example 1 will be described. A cross-sectional view showing the lens configuration of the imaging lens of Example 1 is shown in FIG. In FIG. 1 and FIG. 2 corresponding to Example 2 described later, the left side is the object side and the right side is the image side, and the illustrated aperture stop St does not necessarily represent the size or shape, but the optical axis. This indicates the position of the aperture on Z.

  In the imaging lens of Example 1, the front group G1 includes two negative lenses L1a and L1b in order from the object side, and a cemented lens in which the negative lens L1c and the positive lens L1d are cemented in this order from the object side. ing.

  The rear group G2 includes a positive lens L2a and a cemented lens in which a positive lens L2b and a negative lens L2c are cemented in this order from the object side.

Table 1 shows basic lens data of the imaging lens of Example 1, and Table 2 shows data related to the specifications. In the following, the meaning of the symbols in the table will be described using the example 1 as an example, but the same applies to the example 2 .

  In the lens data of Table 1, the surface number column indicates the surface number that sequentially increases toward the image side with the surface of the component closest to the object side as the first, and the curvature radius column indicates the curvature radius of each surface. In the column of the surface interval, the interval on the optical axis Z between each surface and the next surface is shown. The column of n shows the refractive index of each optical element with respect to the d-line (wavelength 587.6 nm), and the column of ν shows the Abbe number of each optical element with respect to the d-line (wavelength 587.6 nm).

  Here, the sign of the radius of curvature is positive when the surface shape is convex on the object side and negative when the surface shape is convex on the image side. The basic lens data includes the aperture stop St and the optical member PP. In the surface number column of the surface corresponding to the aperture stop St, the phrase (aperture) is written together with the surface number.

  In the data relating to the specifications in Table 2, the focal length f ′, the back focus Bf ′, the F value FNo. The value of the total angle of view 2ω is shown.

  In basic lens data, data on specifications, and data on changing surface spacing, degrees are used as the unit of angle, and mm is used as the unit of length, but the optical system is proportionally enlarged or reduced. Other suitable units can also be used.

  The aberration diagrams of the imaging lens of Example 1 are shown in FIG. In addition, in order from the left side in FIG. 6, spherical aberration, astigmatism, and lateral chromatic aberration at the time of focusing on an object having a concave surface with a curvature radius of 0.020 m on the lens side disposed at a distance of 0.012 m are shown. . Each aberration diagram showing spherical aberration and astigmatism shows aberration with d-line (wavelength 587.6 nm) as a reference wavelength. In the spherical aberration diagram, aberrations with respect to the d-line (wavelength 587.6 nm), the C-line (wavelength 656.3 nm), and the F-line (wavelength 486.1 nm) are indicated by a solid line, a long broken line, and a dotted line, respectively. In the astigmatism diagram, sagittal and tangential aberrations are indicated by a solid line and a dotted line, respectively. In the lateral chromatic aberration diagram, the aberrations for the C line (wavelength 656.3 nm) and the F line (wavelength 486.1 nm) are indicated by a long broken line and a dotted line, respectively. FNo. Of the aberration diagram of spherical aberration. Means F value, and ω in other aberration diagrams means half angle of view.

  Since the symbols, meanings, and description methods of each data described in the description of the first embodiment are the same for the following embodiments unless otherwise specified, the redundant description is omitted below.

  Next, the imaging lens of Example 2 will be described. FIG. 2 is a cross-sectional view showing the lens configuration of the imaging lens of the second embodiment. The imaging lens of Example 2 has the same lens configuration as the imaging lens of Example 1. Further, basic lens data of the imaging lens of Example 2 is shown in Table 3, data relating to the specifications is shown in Table 4, and each aberration diagram is shown in FIG.

Table 11 shows values corresponding to the conditional expressions (1) to (5) of the imaging lenses of Example 1 and 2 . In all examples, the d-line is used as the reference wavelength, and the values shown in Table 11 below are at this reference wavelength.

From the above data, it can be seen that all of the imaging lenses of Examples 1 and 2 satisfy the conditional expressions (1) to (5) and are variously corrected imaging lenses.

  Next, an imaging apparatus according to an embodiment of the present invention will be described. First, an example in which the present invention is applied to an endoscope as an embodiment of an imaging apparatus according to the present invention will be described. FIG. 11 shows a schematic overall configuration diagram of the endoscope.

  The endoscope 100 shown in FIG. 11 mainly includes an operation unit 102, an insertion unit 104, and a universal cord 106 connected to a connector unit (not shown). Most of the insertion portion 104 is a flexible portion 107 that bends in an arbitrary direction along the insertion path. A bending portion 108 is connected to the distal end of the flexible portion 107, and a distal end portion 110 is connected to the distal end of the bending portion 108. Has been. The bending portion 108 is provided to direct the distal end portion 110 in a desired direction, and a bending operation can be performed by rotating a bending operation knob 109 provided in the operation portion 102. The imaging lens 1 according to the embodiment of the present invention is disposed at the inner tip of the tip portion 110. FIG. 11 schematically shows the imaging lens 1. Since the endoscope of the present embodiment includes the imaging lens 1 of the present invention, a good image can be acquired.

  Next, an example in which the present invention is applied to an in-vehicle camera as another embodiment of the imaging apparatus will be described. FIG. 12 shows a state in which an in-vehicle camera is mounted on an automobile.

  In FIG. 12, an automobile 200 includes an on-vehicle camera 201 for imaging a blind spot range on the side surface on the passenger seat side, an on-vehicle camera 202 for imaging a blind spot range on the rear side of the automobile 200, and a rear surface of a rearview mirror. An in-vehicle camera 203 is mounted for photographing the same field of view as the driver. The outside camera 201, the outside camera 202, and the inside camera 203 are imaging devices, and include an imaging lens according to an embodiment of the present invention and an imaging device that converts an optical image formed by the imaging lens into an electrical signal. Yes. Since the in-vehicle cameras (the outside cameras 201 and 202 and the in-vehicle camera 203) of the present embodiment include the imaging lens of the present invention, a good image can be acquired.

  The present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, the values of the radius of curvature, the surface spacing, the refractive index, the Abbe number, etc. of each lens component are not limited to the values shown in the above numerical examples, but can take other values.

DESCRIPTION OF SYMBOLS 1 Imaging lens 100 Endoscope 102 Operation part 104 Insertion part 106 Universal code 107 Soft part 108 Bending part 109 Bending operation knob 110 Tip part 200 Car 201, 202 Outside camera 203 In-vehicle camera G1 Front group G2 Rear group PP Optical member L1a- L2c Lens Sim Image surface St Aperture stop Wa Wax light flux wb Light flux of maximum field angle Z Optical axis

Claims (15)

In order from the object side, the front group, an aperture stop, and a rear group having a positive refractive power,
In the front group, in order from the object side, two or more negative lenses, one negative lens, and one positive lens whose d-line reference Abbe number is smaller than the negative lens are cemented in this order from the object side. With a cemented lens,
The rear group includes, in order from the object side, one or more positive lenses, a positive lens and a negative lens which are cemented in this order from the object side, and a cemented lens having a positive refractive power as a whole. An imaging lens characterized by The imaging lens according to claim 1, wherein the following conditional expression (1) is satisfied.
0.30 <f / fb <0.70 (1)
However,
f: focal length of the entire system fb: focal length of the rear group The imaging lens according to claim 1, wherein the following conditional expression (2) is satisfied.
30.00 <νd (R1) −νd (R2) <80.00 (2)
However,
νd (R1): Abbe number of the positive lens in the cemented lens in the rear group νd (R2): Abbe number of the negative lens in the cemented lens in the rear group The imaging lens according to claim 1, wherein the following conditional expression (3) is satisfied.
−3.00 <f / fn <−0.90 (3)
However,
f: focal length of the entire system fn: composite focal length of the two or more negative lenses in the front group The imaging lens according to claim 1, wherein the front group has a negative refractive power. The imaging lens according to claim 1, wherein the following conditional expression (4) is satisfied.
-0.90 <f / fa <0.00 (4)
However,
f: focal length of the entire system fa: focal length of the front group The imaging lens according to claim 1, wherein the following conditional expression (5) is satisfied.
0.00 <νd (F1) −νd (F2) <30.00 (5)
However,
νd (F1): Abbe number of the negative lens in the cemented lens in the front group νd (F2): Abbe number of the positive lens in the cemented lens in the front group 8. The imaging lens according to claim 1, wherein the rear group substantially includes a positive lens and a cemented lens in which a positive lens and a negative lens are cemented in this order from the object side. . 9. The front group substantially includes two negative lenses in order from the object side, and a cemented lens in which a negative lens and a positive lens are cemented in this order from the object side. 9. Imaging lens. The following conditional expression (1-1) set forth in any one imaging lens of claims 1 to 9, satisfying.
0.40 <f / fb <0.60 (1-1)
However,
f: focal length of the entire system fb: focal length of the rear group The following conditional expression (2-1) set forth in any one imaging lens of claims 1 to 10, satisfying.
35.00 <νd (R1) −νd (R2) <75.00 (2-1)
However,
νd (R1): Abbe number of the positive lens in the cemented lens in the rear group νd (R2): Abbe number of the negative lens in the cemented lens in the rear group The following conditional expression (3-1) set forth in any one imaging lens according to claim 1 to 11, satisfying.
−2.50 <f / fn <−1.10 (3-1)
However,
f: focal length of the entire system fn: composite focal length of the two or more negative lenses in the front group The following conditional expression (4-1) set forth in any one imaging lens of claims 1 to 12, satisfying.
−0.80 <f / fa <−0.10 (4-1)
However,
f: focal length of the entire system fa: focal length of the front group The following conditional expression (5-1) set forth in any one imaging lens according to claim 1 to 13, satisfying.
0.00 <νd (F1) −νd (F2) <23.40 (5-1)
However,
νd (F1): Abbe number of the negative lens in the cemented lens in the front group νd (F2): Abbe number of the positive lens in the cemented lens in the front group Imaging apparatus characterized by including an imaging lens of any one of claims 1 14.